Thin film transistor liquid crystal displays (TFT-LCDs) have features of small size, low power consumption and no radiation, and have been widely applied in production and life of customers, for example, in TVs, monitors, as well as portable electronic display products. Major display panel manufacturers are all in their efforts to improve product performances, for example, to reduce power consumption, increase viewing angles, and reduce response time. Improvement on image-sticking is particularly important for a display panel, because presence of image-sticking directly affects display quality of a displayed image.
Image-sticking refers to the phenomenon that, when a liquid crystal panel is switched to a new image after a specific static image which has been displayed (driven) for a long time period, a faint outline of the previously displayed image partly remains visible on the screen of the liquid crystal panel. Image-sticking is the phenomenon that occurs inside a liquid crystal cell. When a liquid crystal panel is switched to display a different new image after long-time display of a static image, the liquid crystal molecules cannot deflect immediately and completely to meet the new image, thus the display effect is disadvantageously affected.
Based on different forms of occurrence, image-sticking can be classified into two types: area image-sticking and line image-sticking.
Image-sticking mechanism studies show that, image-sticking occurs mainly because of the influence by residual electric charges, which include different distributions of ionic impurities inside a liquid crystal cell and the polarization electric charges incurred inside the liquid crystal cell under the action of an external electric field. These residual electric charges will affect the orientations of the liquid crystal at the top and the bottom of the liquid crystal cell, so that image-sticking occurs in the entire panel area, and more severe situation occurs at transitional positions where significant color difference exists between images. Occurrence of image-sticking is also affected by other factors, such as ambient temperature, static picture type, display duration, brightness level, etc.
Typically, after a liquid crystal module is completed by assembling, it is necessary to detect it on several aspects such as picture quality, dusts, foreign bodies, etc., in order to improve quality and yield for liquid crystal modules. Among others, the detection includes detection and evaluation of image-sticking. The liquid crystal module detection environment requires a certain temperature. A traditional image-sticking evaluation system generally consists of two main parts: one is a signal generator; and the other is an external heating and temperature control equipment. Because a heating and temperature-control equipment needs an external high capacity power supply and a complicated temperature control device, the traditional image-sticking detection system thus is usually bulky, of high cost, and inconvenient for moving due to its large volume. This result that the traditional system requires a dedicated evaluation field, and therefore it cannot perform convenient, real-time evaluation, and it is disadvantageous for monitoring image-sticking level at any time.